The present invention relates to a method for adjusting density measurement positions by making use of changes in densities measured by a scanning densitometer, and more particularly to a density measurement position adjustment method suitable when used in order to allow coordinate positions of density measurement points of a sample sheet placed on an X-Y table to be in correspondence with coordinate positions of density measurement reference points of a reference sheet.
In a process for a printing work, a quantity of an ink supplied has been conventionally controlled with a view to checking a sample sheet on which a pattern is printed to maintain the density of the pattern at a predetermined density. Ordinarily, as shown in FIG. 12, on a sample sheet 42, a belt-shaped solid mark 41 having a predetermined width W is printed at the paper end portion at the same process as that for a picture print 40. Densities of respective colors assigned to sections obtained by dividing the solid mark 41 in a length direction are measured. Namely, there is adopted a method to adjust the solid mark 41 of the sample sheet 42 to a predetermined position on the basis of the judgment by the eye, or to cause the paper end of the sample sheet to be in contact with a guide to thereby position and arrange the sample sheet 42 on a table, thus allowing a head unit of a densitometer to scan thereabove to measure densities of respective colors. In this instance, the density of the pattern 40 is represented by the density of the solid mark 41. In such a density measurement method, it is sufficient that the density measurement area of the head unit of the densitometer falls within the width W of the solid mark 41. Since setting is generally made such that the solid mark 41 is broader than the density measurement area of the head unit, the position adjustment is easy.
In accordance with such a conventional density measurement method, however, while the position adjustment is easy, the drawback therewith is that direct control or supervision of a picture is impossible because the density of the picture is represented by the density of the solid mark. Namely, there may occurs an inconvenience such that the density of an actual pattern fails to clear a prescribed density although the density of the solid mark clears the prescribed density
For directly controlling the density of a pattern, it is required to allow a desired density measurement point (density measurement reference point) of, e.g., a reference sheet, i.e., a specimen sheet on which a pattern satisfying a prescribed density is printed to be precisely in correspondence with a density measurement point of a sample sheet corresponding to the above-mentioned measurement reference point. Namely, when an attempt is made to directly control the density of a pattern, differently from the method to scan a solid mark, there is the possibility that a slight aberation or deviation of a measurement position leads to a large density measurement error. Since the positional relationship between the paper end and the pattern is not necessarily fixed, problem is likely to occur in the adjustment of position of a sample sheet along the guide. Because precision is required for the position adjustment based on the judgment by the eye, its workability is extremely poor.